5.2.1 Collecting Phrases

Phrases for indexing can be collected while writing the document. The
command C-c \ (reftex-index-phrase-selection-or-word)
copies the current selection (if active) or the word near point into the
phrases buffer. It then selects this buffer, so that the phrase line
can be edited. To return to the LaTeX document, press C-c C-c
(reftex-index-phrases-save-and-return).

You can also prepare the list of index phrases in a different way and
copy it into the phrases file. For example you might want to start from
a word list of the document and remove all words which should not be
indexed.

The phrase lines in the phrase buffer must have a specific format.
RefTeX will use font-lock to indicate if a line has the proper
format. A phrase line looks like this:

[key] <TABs> phrase [<TABs> arg[&&arg]... [ || arg]...]

<TABs> stands for white space containing at least one <TAB>.
key must be at the start of the line and is the character
identifying one of the macros defined in the file header. It is
optional; when omitted, the first macro definition line in the file
will be used for this phrase. The phrase is the phrase to be
searched for when indexing. It may contain several words separated by
spaces. By default the search phrase is also the text entered as
argument of the index macro. If you want the index entry to be
different from the search phrase, enter another <TAB> and the index
argument arg. If you want to have each match produce several
index entries, separate the different index arguments with ‘ &&
’1. If you want to be
able to choose at each match between several different index arguments,
separate them with ‘ || ’2. Here is an
example:

So ‘Sun’ will be indexed directly as ‘\index*{Sun}’, while
‘Planet’ will be indexed as ‘\index{Planets}Planet’.
‘Vega’ will be indexed as a subitem of ‘Stars’. The
‘Jupiter’ line will also use the ‘i’ macro as it was the first
macro definition in the file header (see above example). At each
occurrence of ‘Mars’ you will be able choose between indexing it as
a subitem of ‘Planets’, ‘Gods’ or ‘Chocolate Bars’.
Finally, every occurrence of ‘Pluto’ will be indexed as
‘\index{Planets!Pluto}\index{Kuiper Belt Objects!Pluto}Pluto’
and will therefore create two different index entries.